Cleaning of Oleaginous Water III

ABSTRACT

The present invention comprises a process and apparatus for separation of hydrocarbons from hydrocarbon-containing produced water, wherein in stage  1  the hydrocarbon-containing produced water is supplied with a gas-containing component, whereupon a gas- and hydrocarbon-containing produced water mixture is fed to an inlet tube ( 22, 27 ) in the center of a tank, whereupon the said mixture is tangentially distributed via at least one nozzle ( 7 ) and at least one baffle plate ( 8.1 ), whereupon separated hydrocarbons are conveyed to at least one outlet from the tank and cleaned water is conveyed to an outlet ( 12 ) from the tank.

The present invention comprises a process for separation of hydrocarbonsfrom hydrocarbon-containing produced water as well as apparatus forseparation of hydrocarbons from hydrocarbon-containing produced water.

BACKGROUND

Globally is the water production associated with the oil & gasproduction more than three times higher than the oil production. Thisgives an average water fraction of about 75% of what is produced fromthe wells. The water percentage continues to increase. About ten yearsago was it about 70%. The water fraction increases in proportion to theoil fields being older and decreases in proportion to better methodsbeing developed to handle the reservoir and to new fields beingintroduced. Simultaneously the environmental conditions are being morestrict and more complicated to meet. The challenges for the operatorsare increasing and the need of better, diminished and more costeffective technologies arises. The costs of water treatment participatesin determining how high water content it will be profitable to produce.This will also depend on the oil price.

The purpose of the present invention is to provide a purification systemfor produced water with the main focus at oil installations onshore andoffshore worldwide. Produced water coming up from the well with the wellstream is separated from the oil and gas, and then purified anddischarged to the sea or reinjected into the reservoir. Produced wateris a mixture of formation water, residuals of production chemicals andreinjected water (on installations where this is carried out). Thecontents and composition of produced water vary from field to field andfrom well to well within the same field. In addition will also thecomposition vary over time in one and the same well. Each minute willNorwegian oil platforms treat about 400 m³ water. A constantly moremature Norwegian shelf with less oil and more water has resulted in astrong increase in produced water. In 2007 about 200 million m³ producedwater were treated on the Norwegian shelf. About 90 percent of this wasdischarged to the sea.

SUMMARY OF THE INVENTION

The present invention relates to a process for separation ofhydrocarbons from hydrocarbon-containing produced water, wherein instage 1 a gaseous component is supplied to the hydrocarbon-containingproduced water, whereupon a gas- and hydrocarbon-containing producedwater mixture is fed to an inlet tube (22, 27) in the center of a tank,whereupon the said mixture is tangentially distributed via at least onenozzle (7) and at least one baffle plate (8.1), whereupon separatedhydrocarbons are fed to at least one outlet (10) from the tank andpurified (treated) water is fed to an outlet (12) from the tank. Thepresent invention comprises further a stage 2 where a fraction of agas-containing water mixture from outlet (12) is recirculated via astream (15) and fed to an annulus chamber and further tangentially fedvia at least one nozzle (25) and at least one baffle plate (8.2)countercurrently or cocurrently to the descending water mixture fromstage 1. Stage 3 in the present invention comprises that the watermixture from stage 1 is fed to at least one separate stage, via at leastone separating plate (30) and at least one annulus chamber (28), and isfurther tangentially distributed via at least one nozzle (32) and atleast one baffle plate (8.2). Further in the present invention stage 4comprises a descending water mixture which is fed over a layer of apacking material (11). In the present invention the stages mentionedabove can be carried out in the sequence which is considered as suitablefor the purpose of the invention. Further the various stages can berepeated a number of times if it is considered suitable.

One embodiment of carrying out the present invention for separation ofhydrocarbons from hydrocarbon-containing produced water comprises stage1 where the hydrocarbon-containing produced water is supplied with agas-containing component, whereupon a gas- and hydrocarbon-containingproduced water mixture is fed to an inlet tube (22, 27) in the center ofa tank, whereupon the said mixture is tangentially distributed via atleast one nozzle (7) and at least one baffle plate (8.1); and stage 2where a fraction of a gas-containing water mixture from outlet (12) isrecirculated via a stream (15) and fed to an annulus chamber and furthertangentially fed via at least one nozzle and at least one baffle platecountercurrently or cocurrently to the water mixture descending fromstage 1, whereupon separated hydrocarbons are fed to at least one outletfrom the tank and purified (treated) water is fed to an outlet (12) fromthe tank.

One embodiment of the present invention comprises a process forseparation of hydrocarbons from hydrocarbon-containing produced water,comprising stage 1 where the hydrocarbon-containing produced water issupplied with a gas-containing component, whereupon a gas- andhydrocarbon-containing produced water mixture is fed to an inlet tube(22, 27) in a tank, whereupon the said mixture is tangentiallydistributed via at least one nozzle (7) and at least one baffle plate(8.1), whereupon separated hydrocarbons are fed to at least one outletfrom the tank and purified (treated) water is fed from an outlet (12)from the tank; and stage 2 where a fraction of gas-containing watermixture from outlet (12) is recirculated via a stream (15) and is fed toan annulus chamber (23) and further fed tangentially via at least onenozzle (25) and at least one baffle plate (8.2) countercurrently orcocurrently to a water mixture descending from stage 1; and stage 4where the descending water mixture is fed over a layer of a packingmaterial (11) and purified (treated) water is conveyed to outlet (12).

One embodiment of the present invention relates to a process forseparation of hydrocarbons from hydrocarbon-containing produced water,comprising stage 1 where the hydrocarbon-containing produced water issupplied with a gas-containing component, whereupon a gas- andhydrocarbon-containing produced water mixture is fed to an inlet tube(22, 27) in a tank, whereupon the said mixture is tangentiallydistributed via at least one nozzle (7) and at least one baffle plate(8.1), whereupon separated hydrocarbons are fed to at least one outletfrom the tank; and stage 3 where the water mixture from stage 1 is fedto at least one separate stage, via at least one separation plate (30)and at least one annulus chamber (28), and further tangentiallydistributed via at least one nozzle (32) and at least one baffle plate(8.2), whereupon separated hydrocarbons are conveyed to at least oneoutlet (35, 36) from the tank, and purified (treated) water is conveyedto outlet (12) from the tank.

In one embodiment the present invention comprises a process forseparation of hydrocarbons from hydrocarbon-containing produced watercomprising stage 1 where the hydrocarbon-containing produced water issupplied with a gas-containing component, whereupon a gas- andhydrocarbon-containing produced water mixture is fed to an inlet tube(22, 27) in a tank, whereupon the said mixture is tangentiallydistributed via at least one nozzle (7) and at least one baffle plate(8.1) whereupon separated hydrocarbons are fed to at least one outletfrom the tank, and stage 3 where the water mixture from stage 1 is fedto at least one separate stage, via at least one separation plate (30)and at least one annulus chamber (28), and is further tangentiallydistributed via at least one nozzle (32) and at least one baffle plate(8.2), and separated hydrocarbons are fed to at least one outlet (35,36) from the tank; and stage 4 where a descending water mixture is fedover a layer of a packing material (11) and purified (treated) water isfed to an outlet (12) from the tank.

In an embodiment the present process for separation of hydrocarbons fromhydrocarbon-containing produced water comprises stage 1 where thehydrocarbon-containing produced water is supplied with a gas-containingcomponent, whereupon a gas- and hydrocarbon-containing produced watermixture is fed to an inlet tube (22, 27) in a tank, whereupon the saidmixture is tangentially distributed via at least one nozzle (7) and atleast one baffle plate (8.1), whereupon separated hydrocarbons are fedto at least one outlet from the tank; and stage 4 where a descendingwater mixture is fed over a layer of a packing material, and purifiedwater is fed to an outlet (12) from the tank.

In the present invention, the hydrocarbon-containing produced water isfurther distributed via at least one branch means (26) in the topportion of the inlet tube (22, 27). A further gas supply (34) iseffected in the annulus chamber (28). In the invention described abovethe gas-containing component is supplied via an extern supply (2) or isrecirculated from the top of the tank (4). Further gas supply can bechosen from the group comprising as follows; nitrogen, hydrocarbon (fuelgas), CO₂.

Further, an embodiment of the present invention is described where thewater mixture from stage 1 is supplied/streams into an annulus chamberand further into an inlet tube prior to tangential distribution via atleast one nozzle (32) and at least one baffle plate (8.2) in at leastone separate stage.

In an embodiment of the present invention, a flocculant can be addedupstream from the inlet tube (22, 27) for better output.

The present invention describes apparatus for separation of hydrocarbonsfrom hydrocarbon-containing produced water, where the apparatuscomprises the following:

a pressure tank,

at least one inlet tube (22, 27) in the tank,

at least a further branch means (26) in the top portion of the inlettube, at least one nozzle (7) and at least one baffle plate (8.1);

at least one outlet (12) from the tank for purified water;

at least one outlet (10, 35, 36) for separated hydrocarbons.

Apparatus according to the present invention further comprises anannulus chamber (23) which encircles the inlet tube (22) and whichcomprises at least one branch means (24) at least at one level, furthercomprising at least one nozzle (25) and optionally encircled by a screenmeans and at least one baffle plate (8.2). The apparatus is furtherdescribed to comprise at least one separation plate (30) and at leastone annulus chamber (28) encircling the inlet tube (27) with at leastone branch means (31) at least at one level, comprising at least onenozzle (32) and at least one baffle plate (8.2). A layer comprising apacking material is also described according to the invention.

Apparatus for separation of hydrocarbons from hydrocarbon-containingproduced water comprises the following:

a pressure tank,

at least one inlet tube (22, 27) in the tank,

at least one further branch means (26) in the top portion of the inlettube, at least one nozzle (7) and at least one baffle plate (8.1);

at least one outlet (12) from the tank for purified water;

at least one outlet (10, 35, 36) for separated hydrocarbons;

an annulus chamber (23) encircling the inlet tube (22) and comprising atleast a branch means (24) at least at one level, further comprising atleast one nozzle (25) and optionally encircled by a screen means and atleast one baffle plate (8.2).

Further, the present apparatus for separation of hydrocarbons fromhydrocarbon-containing produced water describes the following:

a pressure tank,

at least one inlet tube (22, 27) in the tank,

at least one further branch means (26) in the top portion of the inlettube, at least one nozzle (7) and at least one baffle plate (8.1);

at least one outlet (12) from the tank for purified water;

at least one outlet (10, 35, 36) for separated hydrocarbons;

an annulus chamber (23) encircling the inlet tube (22) and comprising atleast one branch means (24), at least at one level, further comprisingat least one nozzle (25) and optionally encircled by a screen means andat least one baffle plate (8.2),

a layer comprising a packing material.

Further, in the present invention it is described apparatus forseparation of hydrocarbons from hydrocarbon-containing produced watercomprising the following:

a pressure tank,

at least one inlet tube (22, 27) in the tank,

at least a further branch means (26) in the top portion of the inlettube, at least one nozzle (7), and at least one baffle plate (8.1);

at least one outlet (12) from the tank for purified water;

at least one outlet (10, 35, 36) for separated hydrocarbons;

at least one plate (30) and at least one annulus chamber (30) encirclingthe inlet tube (27) and having at least one branch means (31), at leastat one level, comprising at least one nozzle (32) and at least onebaffle plate (8.2.).

Apparatus for separation of hydrocarbons from hydrocarbon-containingproduced water according to the invention comprises the following:

a pressure tank,

at least one inlet tube (22, 27) in the tank,

at least a further branch means (26) in the top portion of the inlettube, at least one nozzle (7), and at least one baffle plate (8.1);

at least one outlet (12) from the tank for purified water;

at least one outlet (10, 35, 36) for separated hydrocarbons;

a layer comprising a packing material.

The present invention comprises the following:

A process for separation of hydrocarbons from hydrocarbon-containingproduced water in a three stage process, where

-   -   hydrocarbon-containing produced water is supplied with a        gas-containing component whereupon the gas- and        hydrocarbon-containing produced water mixture is fed to an inlet        tube (22, 27) via the bottom of a tank, whereupon the said        mixture is tangentially distributed via at least one nozzle (7);    -   a gas-containing water mixture is tangentially supplied        countercurrently or cocurrently and distributed via at least one        nozzle (25);    -   the descending liquid stream is fed over a layer of packing        material (11).

Further, the hydrocarbon-containing produced water is additionallydistributed via at least one nozzle means on the top of the inlet tube(26).

The present invention comprises apparatus for separation of hydrocarbonsfrom hydrocarbon-containing produced water, comprising

a pressure tank

at least one inlet center tube in the bottom of the tank

an annulus chamber/tube outside the center tube and having a branchmeans (24) comprising at least one nozzle

packing material (11).

The apparatus according to the invention comprises further distributionmeans on the top of the center tube (26).

SHORT DESCRIPTION OF THE FIGURES

Embodiment of the invention will now be described with reference to thefollowing figures:

FIG. 1 shows a purification system for produced water.

FIG. 2 shows a detail relating to top of nozzle.

FIG. 3 shows a purification system with three stages where stage (37)shown in FIG. 4 is a separate stage which is repeated twice.

FIG. 4 shows a separate stage (37) which can be repeated as many timesas desired.

FIG. 5 shows purification of water from a degassing tank with the topcurves showing hydrocarbon content in produced water that is fed intothe tank and the bottom curves showing the remaining content ofhydrocarbons conveyed to an outlet for purified water.

DETAILED DESCRIPTION

The purpose of the present invention can be achieved by thecharacteristic properties as shown in the following description of theinvention.

In FIG. 1, produced water from oil/water separator or other purificationequipment as hydrocyclones, degassing tank or similar can be fed inthrough inlet (1). This water is supplied with gas via gas injectionpoint (2) and is mixed together with incoming water in a gas mixer (3).Alternatively the gas mixer (3) is replaced with an injector (ejector)having incoming water as driving force and which sucks (4) gas from thetop of the tank. Typical gas amounts added or circulated is from 0.02 to0.2 Sm³ per m³ water. This will vary with how much residue gas ispresent in the incoming water. This mixture of gas and oil-containingwater is fed into an internal center tube in the tank via the bottom(5). In the top of the internal center tube a branch means (6) whichdistributes the water to one or more tubes having outlet nozzles (7) forcontrol of the velocity of gas/water mixture into the tank. These endtangentially along the tank wall. Because of the tangential ending oftubes/nozzles in the tank, a circulation is achieved in the tank andwhich gives a mixing of water, gas and oil. This results in good contactbetween gas bubbles and oil droplets. To evade the water from thenozzles not to go directly downwardly in the tank, but be mixed withincoming water/gas, a baffle plate (8) is mounted under each of theinlets. This leads the water over the next inlet so that water whereingreat gas bubbles have been released becomes mixed with incoming waterfor better mixing/contact between gas and the oil droplets. To achievegood mixing also in the center of the tank an adjustable nozzle means(26) is mounted on the top of the inlet tube (the center tube, the feedtube), see FIG. 2. This spreads liquid/gas mixture from the center andoutwardly and mixes this with the liquid/gas mixture from the nozzletubes (7). Gas with adherent oil droplets will rise to the surface ofthe liquid in the tank and be taken out together with some water in asubmerged outlet (9) in the top of the tank. This discharge iscontrolled by means of a valve (10). The oil/water mixing ratio in thisstream is dependent of the valve opening.

The water with gas bubbles having a minor ascending velocity than thewater velocity downwardly in the tank will pass a “bed” of packingmaterials selected from the group comprising inter alia Raschig rings(11) or similar and to which gas bubbles with adhered oil is attachedto, further growing together and therewith achieve a buoyancy whichsurpass the descending water velocity and float up to the surface. Pure(treated) water which is supplied from this “bed” will pass out in theoutlet (12) in the bottom of the tank and further for emission (13) oroptionally injection into the reservoir as pressure support. This amountis measured on the flow meter (14). A partial stream (15) from the wateroutlet from the tank will, by means of a pump (16), be circulated backinto the tank. The amount which is recirculated is controlled by meansof a valve (17). Gas via an injection point (18) is supplied and is tothis stream subsequently fed through a mixer (19) which mixes the gasinto the water. Alternatively can gas be sucked from the top of the tank(20) by means of an injector which replaces the mixer (19). Typical gasamount will be 0.05 to 0.3 Sm³ per m³ water. Typical recirculationamount will be 30 to 70% of the maximum design rate for the tank. Theamount of recirculation will be read from the flow meter (21). Outsidethe inner tube (22) is an external tube which in both ends is sealedagainst the inner tube. Thereby a chamber (23) is formed between thesetubes into which the recirculation stream (15) enters. In the top ofthis chamber is a branch means (24) which distribute the water to one ormore tubes having outlet nozzles (25) for control of the velocity of thegas/water mixture into the tank. These end tangentially along the tankwall. To evade that the water from the nozzles not to go directlydownwardly in the tank, but be mixed with incoming water/gas, is atleast one baffle plate (8.2) mounted below each of the inlets. Thisleads the water over the next inlet so that water wherein large gasbubbles having been released are being mixed with the incoming water forbetter mixing/contact between gas and the oil droplets. Alternativelycan this stream be distributed tangentially at any distance from thecenter tube (the inlet tube, the feed tube) with underlying baffle plateand an external vertical wall. Alternatively this stream can also bedistributed vertically upwardly from the outlet of the center tube.Alternatively the distributions mentioned above can be directedcountercurrently to the described distribution relating to the outletnozzles (7). In this regard water being separated from the upper nozzlesystem/mixing supplied with pure water/gas mixture and oil which mightfollow this water, will again be in contact with gas bubbles whichbecome mixed into the water and therewith achieve a new contact zone foroil/gas which results in a better purification. Alternatively afractional stream of incoming water can be fed through the same inlet.Water which is fed via the recirculation will follow the water phase out(12) in the bottom of the tank. To increase the size of the oil dropletsin the incoming water chemicals can be added, for example flocculants,upstream from the unit.

For increased purification a number of tanks can be connected in series.

Alternatively, each separate nozzle can have an injector which sucks gasvia a tube from top of the tank. This tube can be situated outside orinside in the tank.

Alternatively, the inlet tube can extend from the top of the tank anddownwardly. Alternatively the water can be purified in a number ofstages internally in the tank, in which water from the upperpurification stage via nozzles (7) is passed via an annulus chamber (28)between the feed tube (27) and an externally located tube (29) and wherethe upper chamber is separated by means of plate (30). Before the waterenters the said annulus chamber a vortex breaker (38) is present whichprevent water from the center of the tank entering the annulus chamber.This is to avoid entrainment of oil from the top of the tank. The wateris fed therefrom via the branch means (31) which distributes the waterto one or more tubes having outlet nozzles (32) for control of thevelocity of gas/water mixture into a novel chamber. These nozzles endtangentially along the tank wall. Alternatively gas can be supplied tothis stream via gas addition (34). A typical gas is nitrogen,hydrocarbon gas (fuel gas), CO₂, but are not restricted to these. Oiland gas which is separated in this chamber is removed via reject outlet36 and is combined with reject outlets 20 and 35. Alternatively a numberof separate stages as previously described can be installed below eachother where in these stages have the similar function.

Therefore, the present invention provides a solution which renders theinstallation more compact and more effective. Prior art within thisfield uses a number of purification stages in series. This presentsolution has a number of purification stages within the same tank. Itshall further be specified that the present invention can be carried outwith the purification stages mentioned above in the sequence and in thenumber which is considered suitable. This will reduce the costs, reducenecessary required space and therefore be opportune for more customers.Because of its design will it be simpler to build (fabricate) and alsoeasier to be adapted into existing installations than tanks with forexample external tangential inlet.

The present process and apparatus comprise the following:

Process and apparatus for separation of oil/hydrocarbons in liquid stateor gaseous state from produced water in oil production, separation ofother liquids/gases with specific weight difference and which are notdissolved in each other, consisting of:

a. A vertical pressure tank with different height/diameter ratiodependent on what is to be separated.b. Where the inlet stream consisting of what is to be separated, is fedinto a center tube (inlet tube, feed tube) in the bottom of the tankwith the possibility of addition of gas via recirculating from the topof the tank via an ejector (eductor) or additional external gas as forexample nitrogen, carbon dioxide, hydrocarbon gas which for example isseparated from production separators, but which are not restricted tothese.c. A distribution means in the top of inlet tube above described in itemb. and which distribute the feed into one or more feed tubes which endparallel to the tube wall in the upper portion of the tank and at leastone baffle plate below these and which directs the stream from at leastone distribution tube over the next distribution tube to create a spin(circulation) in the tank and a homogenous stream which gives goodmixing of gas/liquid in this portion of the tank.d. An adjustable nozzle means mounted on the top of the inlet tubedescribed in item b. above. This means spreads the liquid/gas mixturefrom the center and outwardly in the tank and mixes with the liquid/gasmixture from the nozzle tube described in item c.e. A tube outside the feed tube described in item c and which is sealedin both ends against the feed tube described in item c and forms anannulus chamber where a recirculated stream from the purified wateroutlet can be recirculated together with gas added into a mixer or withrecirculated gas from the top of the tank via an ejector. Alternativelya portion of the feed stream can be fed into the described annulus tube.f. Where the described annulus tube has a distribution means asdescribed in item c, but placed lower than distribution tube describedin c where the feed stream can be tangentially distributed in anydistance from the center tube towards the tank wall directionallycontrolled cocurrently or countercurrently to the distribution streamdescribed in item c. The baffle plate has an outer vertical wall whichis 2 to 10 times higher than the distribution tube by distributionnearer a tank wall. Alternatively the distribution tubes can be directedhorizontally upwards.g. Where purified liquid outlet is in the bottom of the tank.h. Where downwardly flowing liquid stream passes a “bed” of gascoalescent material (packing material) where small gas bubbles withadherent droplets/particles are built together to large ones and aregiven buoyancy to rise to the surface.i. Where gas and oil which has been separated are removed from the topof the tank via a submerged tube at a level of between 5 and 20% of thetank height from the top of the tank where the removed amount isregulated by means of a valve.j. A gas “pad” in the top of the tank is formed due to the tubedescribed in item i., which is a buffer for recirculation of gas.k. Where the pressure in the tank is controlled by means of a valve inthe outlet tube.

FIG. 5 shows purification of water from a degassing tank where the topcurves show hydrocarbon content in produced water which is fed into thetank. In particular, FIG. 5 shows the effect of the process forseparation of hydrocarbons from hydrocarbon-containing produced waterwhere the water has been supplied with a gas-containing component, andwhere the gas- and hydrocarbon-containing produced water mixture hasbeen fed to an inlet tube in the center of a tank. Further, the saidmixture has been tangentially distributed via at least one nozzle and atleast one baffle plate, and the separated hydrocarbons has been conveyedto an outlet from the tank and purified water has been conveyed to anoutlet from the tank. The curves at the bottom show the remainingcontent of hydrocarbons conveyed to an outlet for purified water.

It is important to notice that further purification stages can beeffected in relation to the various stages and the embodiments asdescribed in the foregoing.

When preferred embodiments of the present invention have been described,it will for the person skilled in the art be evident that otherembodiments which incorporate the concepts can be used. These andexample illustrated in the foregoing are considered as mere example andthe factual scope of the invention shall be determined from thefollowing patent claims.

1. A method for separating oil from oil-containing water in a vesselcomprising an upper chamber and a lower chamber, the method comprising:injecting gas into the oil-containing water to generate anoil-containing water and gas mixture; tangentially distributing theoil-containing water and gas mixture into the upper chamber; separatingoil and gas from the oil-containing water and gas mixture in the upperchamber to produce a partially-cleaned water to be distributed in thelower chamber; outputting separated oil and gas in the upper chamberthrough an upper oil outlet; tangentially distributing thepartially-cleaned water into the lower chamber; separating oil and gasfrom the partially-cleaned water in the lower chamber to produce acleaned water; outputting separated oil and gas in the lower chamberthrough a lower oil outlet.
 2. The method of claim 1, further comprisingoutputting the cleaned water in the lower chamber through a wateroutlet.
 3. The method of claim 1, wherein the vessel further comprises aseparation plate defining the upper chamber and lower chamber.
 4. Themethod of claim 1, wherein the upper chamber and lower chamber are influid communication.
 5. The method of claim 1, wherein tangentiallydistributing the oil-containing water and gas mixture into the upperchamber comprises distributing the oil-containing water via an uppernozzle located in the upper chamber and extending from an inlet tubeextending through the tank.
 6. The method of claim 5, further comprisinga plurality of upper nozzles.
 7. The method of claim 1, whereintangentially distributing the partially-cleaned water into the lowerchamber comprises distributing the partially-cleaned water via a lowernozzle located in the lower chamber and extending from a separationplate located in the vessel.
 8. The method of claim 7, furthercomprising a plurality of lower nozzles.
 9. The method of claim 1,further comprising flowing the cleaned water through a bed of gascoalescent material in the lower chamber.
 10. The method of claim 2,further comprising controlling flow of the outputted clean water via avalve in the water outlet.
 11. The method of claim 1, wherein separatingoil and gas from the oil-containing water and gas mixture in the upperchamber to produce a partially-cleaned water to be distributed in thelower chamber further comprises passing the oil-containing water and gasmixture over a baffle plate in the upper chamber.
 12. The method ofclaim 1, wherein separating oil and gas from partially-cleaned water inthe lower chamber to produce cleaned water further comprises passing thepartially-cleaned water over a baffle plate in the lower chamber.